This invention generally relates to a method for the synthesis of oxide nanoparticles. More specifically, it relates to oxide nanoparticles synthesized in an essentially water free environment.
There is a great deal of interest in particulate materials in a controlled fashion with particle sizes less than about 1000 nm, commonly referred to as nanoparticles. Nanoparticles exhibit a unique size dependence on their physical properties, such as bandgap, superparamagnetism, and optical properties. Nanoparticles are also interesting as fillers due to their extremely high surface/volume ratios and the fact that, due to their size, they scatter visible light poorly.
Conventionally, metal oxide particles may be prepared by precipitation from aqueous solutions, for example, when a soluble metal salt solution undergoes a pH change. Nitrate, carbonate, oxalate, and similar metal salts may be thermally decomposed to yield oxides from aqueous solutions as well. The book entitled “Treatise in Inorganic Chemistry”, by H. Remy, translated by J. S. Anderson and edited by J. Kleinberg, Elsevier, 1956 discusses such methods. In these processes, water is unavoidably retained in the particulate oxide particle. Residual proton content is very difficult to eliminate.
The sol gel process is well known for producing hydrous metal oxides, which can then be calcined, but also invariably contain excess hydrogen in the product. This method has also been used to produce various metal oxide nanoparticles, and even metal oxide coatings of nanoparticles, with mixed results. In one case, a substoichiometric amount of water is used in the hydrolysis of alkoxide precursors to form titania nanoparticles.
Previous methods for producing hydrous metal oxides can cause difficulty in forming oxide nanoparticles due to the continuing presence of water. Thus, there remains a need to produce oxide nanoparticles using precursors similar to those used in a sol-gel process without addition of water for hydrolysis of the precursor.